In recent years, many networking and telecommunications carriers have deployed Pseudowires to carry Layer-2 (also known as the data link layer of the Open Systems Interconnection (OSI) Reference Model) traffic. A Pseudowire (PW) refers to an emulation of a native service over a network. Examples of the native service include Asynchronous Transfer Mode (ATM), Frame Relay, Ethernet, Time Division Multiplexing (TDM), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), etc. Examples of the network include Multiprotocol Label Switching (MPLS), Internet Protocol (IP), etc. More recently, a number of carriers have extended the use of Pseudowires beyond packet encapsulation, and offered Pseudowires as a type of network service. Consequently, data traffic protection and redundancy in environments that use Pseudowire have become critical.
At the edge of a network, a network edge device such as an edge router may receive multiple Layer-2 flows (also referred to as Attachment Circuits (ACs)). In a typical network supporting Pseudowires, each AC is mapped to a Pseudowire. Ingress packets received mapped to a specific Pseudowire are labeled with an identifier associated with this Pseudowire, and are switched via the Pseudowire. A physical link may support one or more Pseudowires. Ideally, the data flow in a Pseudowire should be protected. In other words, if an active Pseudowire fails, the data flow should be redirected to an alternative Pseudowire to avoid data loss.
Pseudowires can operate over many physical media types. However, existing Pseudowire systems typically provide no protection or very limited protection. For example, there is usually no data protection for Pseudowires on different physical media types, since most network protection schemes, such as APS for SONET, Link Aggregation for Ethernet, do not apply over multiple physical media types.
Some MPLS devices implement schemes such as MPLS Fast Reroute to provide limited data protection. These existing schemes, however, often do not provide adequate protection. Take the following scenario as an example: between two provider edges (PEs), a first tunnel comprising multiple Pseudowires is protected by a second tunnel. Due to network topology constraints, the two tunnels may have different bandwidth. This is a possible scenario in an MPLS Fast Reroute operation. In this example, the second tunnel may have lower bandwidth than that of the first one. If the first tunnel should fail, the amount of data that needs to be redirected through the second tunnel may exceed the capacity of the second tunnel. Furthermore, existing protocols typically do not provide a way of determining which data gets priority. Thus, certain mission critical data may be dropped while other less critical data may pass through.
It would be desirable to have a way to provide better Pseudowire protection and to have more control during switchover. It would also be desirable if the protection scheme could be implemented without significant changes to existing protocols and devices.